Electric machine with de-excitation valve

Abstract

This electrical machine comprises a rotor (7), a stator (2), and a vacuum chamber (10), the rotor (7) and / or the stator (2) comprising a superconducting material, the rotor (7) and / or the stator (2) comprising the superconducting material being placed within the vacuum chamber (10), the electrical machine further comprising a cooling system (11) for the rotor and / or the stator located within the vacuum chamber (10) and a valve (12) located through a peripheral wall (13) of the vacuum chamber (10). Figure for the abbreviation: Fig 2

Description

Title of the invention: Electric machine with de-excitation valve technical field

[0001] The present invention relates to the de-excitation of superconducting electrical machines.

[0002] The present invention is applicable to fully or partially superconducting electrical machines, in configurations in which the armature or the inductor alone can (may) be superconducting.

[0003] A particularly interesting application of the invention relates to turbomachines intended for supplying aircraft onboard networks with electrical energy. Previous techniques

[0004] Electric or hybrid aircraft propulsion systems require the use of electric motors capable of competing with, or even exceeding, the performance of internal combustion engines.

[0005] Electric machines intended for the propulsion of electric aircraft are characterized by electrical power densities exceeding approximately 20 kW per kg-

[0006] In this context, the use of the most efficient machines possible is advantageous in order to be able to achieve these levels of power density.

[0007] The use of superconducting machines allows, firstly, for good efficiency to be obtained.

[0008] Indeed, when cooled to a temperature below their critical temperature, superconducting materials have zero resistivity, which allows direct currents to flow without loss.

[0009] At this temperature, they also exhibit a diamagnetic response to any variation in the magnetic field. This behavior is analogous to that of a magnetic field barrier.

[0010] The absence of resistivity of superconducting materials at a temperature below their critical temperature therefore makes it possible to increase the current density flowing in the conductors.

[0011] Indeed, the absence of Joule heating losses in superconducting conductors prevents a linear increase in cooling requirements with increasing power of superconducting electric motors. Nevertheless, it remains necessary to cool them to temperatures below their critical temperatures, typically below 100 Kelvin or even 150 Kelvin.

[0012] Figure 1 shows an example of an embodiment of a superconducting electrical machine 1 with flux barriers and axial flux without a magnetic core, also called an iron-free machine. Figure 1 illustrates in particular the rotor and stator of such an electrical machine 1.

[0013] The electrical machine 1 comprises a stator 2 including an annular superconducting inductor 3 and one or more arrangements 5 of electromagnetic coils 6 forming an armature, the inductor 3 being coaxial with the arrangements 5 of electromagnetic coils 6. More specifically, the stator 2 includes a part of the inductor 3. In particular, the part of the inductor 3 included in the stator 2 includes, for example, a direct current superconducting coil.

[0014] The electric machine also includes a rotor 7 comprising radially arranged superconducting pellets 8 within the annular inductor and rotating relative to the stator 2. The inductor 3 thus comprises a DC superconducting coil 3 located in the stator 2 and superconducting pellets 8 located in the rotor 7. The axis of rotation of the rotor corresponds to the axial flux axis of the electric machine 1. The superconducting pellets 8 are cooled, for example with helium, nitrogen, or hydrogen, and achieve the variation of the magnetic field through the diamagnetic response of the superconducting pellets 8. The superconducting pellets 8 may, for example, have a circular shape or an annular cross-section, the latter shape improving the power density of the electric machine.

[0015] The example most particularly illustrated in [Fig. 1] corresponds to an axial flux machine comprising a rotor 7 flanked by two stators 2. In this case, a set of pads 8 is flanked on either side by an arrangement 5 of electromagnetic coils 6. Alternatively, one could also have a stator flanked by two rotors. In this variant, an arrangement 5 of electromagnetic coils is flanked on either side by a set of superconducting pads 8.

[0016] In a generator operating mode, the inductor 3 creates an intense magnetic field, the superconducting pellets 8 cause the variation of this magnetic field, and the electromagnetic coils 6 are exposed to the varying magnetic field created by the rotation of the rotor 7. An electromotive force is thus generated according to Faraday's law.

[0017] In the context of aviation, fault management within electrical machines is essential to guarantee the overall reliability of aircraft. In the event of a fault, it is imperative to limit its impact. For example, a defective electrical generator machine that continues to rotate can disrupt surrounding systems by injecting unwanted and uncontrolled currents or voltages.

[0018] Solutions exist to limit the impact of an electrical machine failure. One mechanical solution consists of segmenting a machine shaft to prevent drive in the event of a failure, although this results in the destruction of the machine shaft. An electromagnetic solution consists of switching off the sources of magnetic fields, for example, magnets or electromagnets.

[0019] However, these solutions are not directly applicable to superconducting electrical machines, which usually require vacuum insulation and cooling. Indeed, the strong magnetic fields used in superconducting machines complicate their demagnetization. Description of the invention

[0020] The present invention therefore aims to overcome the aforementioned disadvantages and to facilitate a rapid and reliable de-excitation of an electrical machine, for example during a breakdown.

[0021] The present invention relates to an electrical machine comprising a rotor, a stator, and a vacuum chamber, the rotor and / or the stator comprising a superconducting material, the rotor and / or the stator which comprises the superconducting material being placed in the vacuum chamber, the electrical machine further comprising a cooling system for the rotor and / or the stator placed in the vacuum chamber, and a valve placed through a peripheral wall of the vacuum chamber.

[0022] Thus, in the event of a failure, opening the valve allows the inside of the vacuum chamber to be connected to the outside in order to rapidly increase the internal temperature of the chamber and eliminate the superconducting effects of the superconducting material. Indeed, the thermal insulation provided by the vacuum is broken, and heat transfer by convection occurs between the air and the rotor and / or the stator.

[0023] Advantageously, the vacuum chamber is placed in an environment comprising air whose temperature is at least 5 Kelvin higher than the temperature of the rotor and / or stator placed in the vacuum chamber.

[0024] In one embodiment, the electric machine further includes a solenoid valve controlling the opening and closing of the valve according to a setpoint.

[0025] Advantageously, the vacuum chamber includes a temperature sensor.

[0026] In one embodiment, the stator comprises an annular inductor and an armature comprising at least one arrangement of electromagnetic coils, and wherein the rotor comprises superconducting pads mounted radially inside the inductor.

[0027] Advantageously, the inductor is made of superconducting material.

[0028] The invention also relates to a turbomachine comprising at least one electrical machine as defined above.

[0029] In addition, the invention also relates to an aircraft comprising at least one turbomachine as defined above.

[0030] The invention also relates to a method for de-exciting an electrical machine as defined above, the method comprising the following steps: - Detection of a fault in the electrical machine; and - Opening the valve until the temperature of the rotor and / or stator placed in the vacuum chamber beyond a predefined temperature threshold for which the superconducting material no longer has a superconducting effect. Brief description of the drawings

[0031] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0032] [Fig. 1] which has already been mentioned, schematically illustrates in exploded view the rotor and stator of an electrical machine with flux barriers according to the prior art;

[0033] [Fig.2] schematically illustrates one embodiment of an electrical machine according to the invention; and

[0034] [Fig.3] illustrates the steps of the process according to the invention. Detailed description of at least one embodiment

[0035] A simplified diagram of an embodiment of an electrical machine 1 is schematically represented in [Fig.2].

[0036] The rotor 7 and stator 2 visible in [Fig. 1] represent a particular embodiment of the rotor 7 and stator 2 of the electric machine 1 illustrated in [Fig. 2]. Any other superconducting machine or any other rotor and stator arrangement may also be suitable.

[0037] Said electrical machine 1 therefore comprises a rotor 7, a stator 2, a vacuum chamber 10 and a cooling system 11.

[0038] In this embodiment, the rotor 7 and the stator 2 each comprise an element of superconducting material.

[0039] As illustrated in [Fig.1], the stator 2 comprises for example a superconducting annular inductor 3 and an armature comprising at least one arrangement 5 of electromagnetic coils 6.

[0040] The rotor 7 includes, for example, superconducting pads 8 mounted radially inside the inductor 3 of the stator 2.

[0041] In this embodiment, the rotor 7 and the stator 2 are placed within the vacuum chamber 10 and the vacuum chamber 10 is connected to the cooling system 11. In operation, the electric machine 1 places the vacuum chamber 10 under vacuum and cools the rotor 7 and the stator 2 using the cooling system 11 in order to promote the superconducting behaviors of the stator 2 and the rotor 7.

[0042] In another embodiment, only the rotor 7 comprises a superconducting element. In this embodiment, only the rotor 7 is placed in the vacuum chamber 10 and only the rotor 7 is cooled.

[0043] Conversely, in a final embodiment, only the stator 2 comprises a superconducting element and only the stator 2 is placed in the vacuum chamber 10 to be cooled.

[0044] In the embodiment illustrated in [Fig. 2], the electric machine 1 includes a valve 12 positioned through a wall 13 of the vacuum chamber 10. In particular, the wall 13 of the vacuum chamber 10 is perforated to allow the valve 12 to be inserted. The valve 12 can thus be introduced into existing vacuum chambers for electric machines, simply and at low cost. The valve 12 can reach an open position and a closed position.

[0045] In its closed position, the valve 12 keeps the vacuum chamber 10 airtight. In its open position, the valve 12 creates a communication between the inside and outside of the vacuum chamber 10.

[0046] Depending on the desired vacuum quality inside the vacuum chamber 10, active pumping by a pump within the vacuum chamber may be necessary to maintain the vacuum inside the chamber. When the valve 12 is opened, there are two possible scenarios. In one implementation, the pump is active and draws in air, which will enter the chamber even more rapidly (accelerating heating). In another implementation, the pump can be switched off at the same time as the valve 12 is opened.

[0047] During the operation of the electric machine 1, the valve 12 is in the closed position. If it is desired to de-energize the electric machine 1, for example if a fault is detected, the valve 12 is opened. The vacuum in the vacuum chamber 10 creates suction, and air outside the vacuum chamber 10 enters the vacuum chamber 10 and increases the internal temperature of the rotor and stator in the vacuum chamber 10 due to the loss of thermal insulation provided by the vacuum.

[0048] In particular, the vacuum chamber 10 is preferably placed in an environment containing air whose temperature is at least 5 Kelvin higher than the internal temperature of the vacuum chamber 10 when it is cooled. In this way, opening the valve 12 ensures an increase in the internal temperature of the vacuum chamber 10.

[0049] For a superconducting material maintained at its critical operating temperature, for example 50 Kelvin, an increase of 5 Kelvin is sufficient to suppress the superconducting effect and thus de-excite the electrical machine 1.

[0050] The valve 10 is, for example, kept open for the time necessary for the temperature to rise. The vacuum chamber 10 includes, for example, a temperature sensor 15, for example a thermocouple, in order to provide temperature information to a remote computer 16 controlling the de-excitation of the electric machine 1. In one embodiment, the temperature sensor is placed on the rotor and / or the stator, so as to accurately measure their temperature.

[0051] In addition, the electric machine 1 includes a solenoid valve 17 controlling the opening and closing of the valve 12. The solenoid valve 17 is, for example, controlled by a command sent from the remote computer 16.

[0052] The remote computer 16 implements a method of de-exciting the electrical machine 1 by implementing a first step 21 of detecting a fault in the electrical machine 1. The fault may originate from a mechanical or electrical problem.

[0053] Then, a step 22 of opening the valve 12 is performed while the internal temperature of the vacuum chamber 10 rises above a predefined temperature threshold. For example, an operator predefines in the remote computer 16 a temperature at which the superconducting materials no longer have any effect. The temperature sensor 15 measures the temperature and sends it to the remote computer 16.

[0054] Optionally, a step 23 of stopping the cooling system 11 is carried out in parallel with the opening of the valve 12 in order to accelerate the increase in the internal temperature of the vacuum chamber 10.

Claims

Demands

1. An electrical machine comprising a rotor (7), a stator (2), and a vacuum chamber (10), the rotor (7) and / or the stator (2) comprising a superconducting material, the rotor (7) and / or the stator (2) comprising the superconducting material being located in the vacuum chamber (10), characterized in that it further comprises a cooling system (11) for the rotor and / or the stator located in the vacuum chamber (10) and a valve (12) located through a peripheral wall (13) of the vacuum chamber (10), the vacuum chamber (10) being located in an environment comprising air having a temperature at least 5 Kelvin higher than the temperature of the rotor and / or the stator located in the vacuum chamber (10), the vacuum chamber (10) comprising a pump configured to maintain a vacuum inside said vacuum chamber (10) and to draw in air entering through the valve (12) open.

2. An electric machine according to claim 1, comprising a solenoid valve (17) controlling the opening and closing of the valve (12) according to a setpoint.

3. An electrical machine according to any one of claims 1 and 2, wherein the vacuum chamber (10) includes a temperature sensor (15).

4. An electric machine according to any one of claims 1 to 3, wherein the stator (2) comprises an annular inductor (3) and an armature comprising at least one arrangement (5) of electromagnetic coils (6), and wherein the rotor (7) comprises superconducting pellets (8) mounted radially inside the inductor (3).

5. Electric machine according to claim 4, wherein the inductor (3) is made of superconducting material.

6. Turbomachine comprising at least one electric machine (1) according to any one of claims 1 to 5.

7. Aircraft comprising at least one turbomachine according to claim 6.

8. A method for de-exciting an electrical machine (1) according to any one of claims 1 to 5, characterized in that it comprises the following steps: Detection (step 21) of a fault in the electrical machine (1); and Opening (step 22) of the valve (12) until the temperature of the rotor and / or stator placed in the vacuum chamber (10) increases beyond a predefined temperature threshold for which the superconducting material no longer has a superconducting effect.

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